Eye direction detecting apparatus

ABSTRACT

An eye direction detecting apparatus for a camera having a light transferring system for guiding a beam of parallel light rays to an eye of a photographer includes a light receiving system having a light receiving portion on which a first Purkinje image based on specular reflection of a cornea of the eye and reflecting light from a retina of the eye is formed, the light receiving portion generating a light receiving output. The apparatus further includes a processing circuit for detecting the eye direction of the eye based on the light receiving output of the light receiving portion. Further, according to the teachings of the present invention, including an optical member having certain identically inclined surfaces prevents refracted light from forming a ghost image within the light receiving system of an eye direction detecting apparatus.

This application is a continuation of application Ser. No. 08/167,036,filed Dec. 16, 1993, now abandoned, which is a continuation ofapplication Ser. No. 07/982,427, filed Nov. 27, 1992, which issued asU.S. Pat. No. 5,327,191 on Jul. 5, 1991, which is a continuation of Ser.No. 07/576,191, filed Aug. 27, 1990, now abandoned, which is acontinuation of Ser. No. 07/282,035, filed on Dec. 9, 1988, nowabandoned, which is a continuation-in-part of Ser. No. 07/152,359, filedFeb. 4, 1988, now abandoned. The disclosure of application Ser. No.07/152,359 went abandoned in favor of continuation application Ser. No.07/375,564, which went abnadoned in favor of continuation applicationSer. No. 07/520,970, which went abandoned in favor of divisionalapplication Ser. No. 07/575,636, which went abandoned in favor ofcontinuation application Ser. No. 07/926,367, which issued as U.S. Pat.No. 5,291, 234 on Mar. 1, 1994, and is expressly incorporated in itsentirety by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an eye direction detecting apparatus.More particularly, the present invention relates to an eye directiondetecting apparatus suitable for use in a camera having an automaticfocusing device in which focusing zones of an auto focus optical system,each of which focusing zones corresponds to each of various focusingzones of the finder, are located in optically generally conjugatepositions with a plurality of focusing zones disposed within a viewfield of the finder, and focusing is made on an object which is visuallyoverlapped with a focusing zone corresponding to a selected one of thevarious focusing zones of the finder.

2. Description of Related Art

An auto optical focus detecting device for a camera having an auto focusoptical system has heretofore been developed. FIG. 1 is a schematic viewShowing an optical system of an auto optical focus detecting device of,a single-lens reflex camera, for example, which has an auto focusoptical system. In the figure, 1 denotes a photographic lens, 2 asubject to be photographed, 3 a view field mask, 4 a condenser lens, 5 adiaphragm mask, 6 and 7 a separator lens serving as an image splittingoptical element for reimaging, and 8 a CCD serving as an image receivingelement. The view field mask 3, the condenser lens 4, the diaphragm mask5, the separator lenses 6 and 7, and the CCD 8 are integrally modulatedas one unit and constitute an auto focus optical system 9.

In this auto focus optical system 9, the view field mask 3 is disposedin the vicinity of a film equivalent plane 10. The film equivalent plane10 is in a position optically conjugate with the subject 2 to bephotographed through the photographic lens 1. A well focused image 11 ofthe subject 2 is formed on the film equivalent plane 10 when thephotographic lens 1 is in focus. The condenser lens 4 and the diaphragmmask 5 have the function of splitting the photographic light passing onboth right and left sides of the photographic lens 1. The separatorlenses 6 and 7 are in a position optically conjugate with thephotographic lens 1 through a condenser lens 4.

The separator lenses 6 and 7, as shown in FIG. 2, are disposed in thehorizontal direction. Further, the separator lenses 6 and 7 faceimaginary opening areas 14 and 15 of an exit pupil 13 of thephotographic lens 1 through a zone 12 located in a position opticallyconjugate with a center zone of a finder as will be described. Theseparator lenses 6 and 7 intake a bundle of light rays passed throughthe opening areas 14 and 15. The image 11 formed on the film equivalentplane 10 is reimaged as images 11' in two areas on the CCD 8.

Distance between the images 11' well focused (see FIG. 3(a)) isrepresented by l_(o) as shown in FIG. 4. When the photographic lens 1 isfocused in a position in front of the focal point of the aforementionedwell focused image as shown in FIG. 3(b), the distance between theimages 11' becomes less and, as a result, the distance between signals Scorresponding thereto becomes less than the distance l_(o). On the otherhand, when the photographic lens 1 is focused in a position behind thefocal point of the aforementioned well focused image as shown in FIG.3(c), the distance between the images 11' becomes greater and, as aresult, a distance between signals S corresponding thereto becomegreater than the distance l_(o). Since the distance between the images11' is changed in proportion to a defocusing amount of the photographiclens 1, in the conventional auto optical focus detecting device of asingle-lens reflex camera, a distance between images of the CCD 8 isdetected and the signals are arithmetically processed, and thephotographic lens 1 is moved to the focal position with reference to thefocusing direction and defocusing amount of the photographic lens 1.And, as shown for example in FIG. 5, if the optical focus is found byframing such that desired subject 2 to be photographed is located in thecenter zone 17 arranged at the center of the finder 16, the photographiclens 1 is automatically brought into a focusing state. If a photographis taken in the foregoing state, a well focused photograph can beobtained.

In this conventional auto optical focus detecting device of asingle-lens reflex camera, since the zone is located in the center ofthe finder 16, a desired subject 2 will be positioned in the center ofan obtained photograph unless an adequate alternate arrangement is made.There are some instance, it should be noted, where a desired subject 2is preferably positioned in a peripheral area of a photograph instead ofthe center of the photograph. To this end, therefore, in theconventional single-lens reflex camera, a focus lock mechanism isprovided. That is, the subject 2 to be photographed is positioned in thecenter of the finder 16 to automatically find the distance to thesubject 2. In that state, the focus is locked. If a photograph is takenin the framing as shown in FIG. 6, a photograph can be obtained in whicha desired subject 2 is positioned in the peripheral area.

However, in this conventional auto optical focus detecting device of asingle-lens reflex camera, the subject 2 must first be positioned in thecenter of the finder 16. Then, the photographic lens 1 must be moved toa focusing state. In that state, the focus must be locked to fix thephotographic lens 1. Then, the framing must be performed once again.Only thereafter can a photograph be taken. Therefore, much time andlabor are required before the camera is ready to take a photograph.

SUMMARY OF THE INVENTION

It went abandoned in favor of continuation application Ser. No.07/374,564, which went abandoned in favor of continuation applicationSer. No. 07/520,970, which went abandoned in favor of divisionalapplication Ser. No. 07/575,636, which went abandoned in favor ofcontinuation application Ser. No. 07/926,367, which issued as U.S. Pat.No. 5,291,234 on Mar. 1, 1994, and is therefore a first object of thepresent invention (as it is for parent application Ser. No. 07/152,359)to provide an auto optical focus detecting device for a single-lensreflex camera, in which a photographic operation for obtaining aphotograph with a desired subject positioned in a peripheral area can beeasily and rapidly performed.

In order to achieve the first object, an auto optical focus detectingdevice for a camera according to the present invention (and according tothe invention of parent application Ser. No. 07/152,359) comprises acenter zone being located in a center of a view finder-of a camera body;at least two peripheral zones being located in the view finder, one ofthe two peripheral zones being located in the right-hand side withrespect to the center zone and the other being located in the left-handside; the camera body containing a center auto focus system and at leasttwo peripheral auto focus optical systems; the center auto focus opticalsystem having a zone corresponding to the center zone, the zone beingsubstantially conjugate with the center zone; the peripheral auto focusoptical systems, respectively, having a substantially conjugate zonecorresponding to the peripheral zone, each zone being substantiallyconjugate with the peripheral zone; a photographic lens being attachedto the camera body, an exit pupil of the photographic lens beingoptically aligned to project light rays through the center zone of thecenter auto focus optical system, at least two aperture zones beingdefined on the exit pupil by the at least two peripheral auto focusoptical systems, each of the aperture zones being optically aligned toproject light rays through the peripheral zone, at least one of the twoaperture zones being located at an upper side away from a centralportion of the exit pupil and the other being located at a lower sideaway from the central portion; the center auto focus optical system andthe two peripheral auto focus optical systems, respectively, having atleast one photoelectronic device for producing an output signal; and theoutput signal produced by the photoelectronic device being adapted tomove the photographic lens automatically, thereby to bring the camera tobe in focus.

According to this auto optical focus detecting device, when a photographwith a subject to be photographed positioned in a peripheral area isrequired, a distance to the subject can be automatically found by usinga peripheral auto focus optical system adapted to find the distance tothe peripheral area without the aforementioned troublesome photographicprocedure. Therefore, a photograph can be taken rapidly.

In the invention having the above-mentioned embodiment for achieving thefirst object, if the separator lens of the peripheral auto focus opticalsystem is not optically aligned with the exit pupil at predeterminedangles, the image detecting accuracy of the auto focus optical systembecomes poor due to vignetting. Therefore, the angle of the separatorlens with respect to the exit pupil of the photographic lens of theperipheral auto focus optical system must be adjusted each timeaccording to the lens characteristic (for example, whether the lens hasa short focal point or a long focal point) of a photographic lensmounted on a lens mount which is to be attached to and detached from thecamera body.

The fact that the adjustment and/or establishment of the angles for theseparator lens of the peripheral auto focus optical system with respectto the exit pupil of the photographic lens depending on whether thephotographic lens mounted on the lens mount has a short focal point or along focal point must be carried out manually causes much inconveniencewith respect to standardizing a camera body since various kinds of lensgroups are prepared as interchangeable lens mounts which are to beattached to or detached from the camera body.

It is therefore a second object of the present invention (as it is forthe invention of parent application Ser. No. 07/152,359) to provide anauto optical focus detecting device of a camera, in which the adjustmentand/or establishment of angles can be automatically performed such thata direction of a bundle of light rays taken into the peripheral autofocus optical system is directed toward the exit pupil of thephotographic lens according to the attachment of a lens mount to acamera body.

In order to achieve the second object, an auto optical focus detectingdevice of a single-lens reflex camera according to the present invention(and the invention of the parent application Ser. No. 07/152,359)comprises a center zone being located in a center of a view finder of acamera body; at least two peripheral zones being located in the viewfinder, one of the two peripheral zones being located in the right-handside with respect to the center zone and the other being located in theleft-hand side; the camera body containing a center auto focus opticalsystem and at least two peripheral auto focus optical systems; thecenter auto focus optical system having a zone corresponding to thecenter zone, the zone being substantially conjugate with the centerzone; the peripheral auto focus optical systems, respectively, having asubstantially conjugate zone corresponding to the peripheral zone, eachzone being substantially conjugate with the peripheral zone; aphotographic lens being attached to the camera body, an exit pupil ofthe photographic lens being optically aligned to project light raysthrough the center zone of the center auto focus optical system, atleast two aperture zones being defined on the exit pupil by the at leasttwo peripheral auto focus optical systems, each of the aperture zonebeing optically aligned to project light rays through the peripheralzone, at least one of the two aperture zones being located at an upperside away from a central portion of the exit pupil and the other beinglocated at a lower side away from the central portion; the center autofocus optical system and the two peripheral auto focus optical systems,respectively, having at least one photoelectronic device for producingan output signal; and the output signal produced by the photoelectronicdevice being adapted to move the photographic lens automatically,thereby to bring the camera into focus, each of the peripheral autofocus optical systems comprising a focus unit, the camera body having atleast one optical member which is located in front of the focus unit,and the optical member changing a direction of a bundle of light rayscoming through the aperture zone, thus the bundle of light rays comingthrough the aperture zone being automatically made incident to the zoneof each peripheral auto focus optical system according to thephotographic lens characteristic.

As another embodiment for achieving the second object, an auto opticalfocus detecting device of a single-lens reflex camera according to thepresent invention (and the invention of parent application Ser. No.07/153,359) comprises a center zone being located in a center of a viewfinder of a camera body; at least two peripheral zones being located inthe view finder, one of the two peripheral zones being located in theright-hand side with respect to the center zone and the other beinglocated in the left-hand side; the camera body containing a center autofocus optical system and at least two peripheral auto focus opticalsystems; the center auto focus optical system having a zonecorresponding to the center zone, the zone being substantially conjugatewith the center zone; the peripheral auto focus optical systems,respectively, having a substantially conjugate zone corresponding to theperipheral zone, each zone being substantially conjugate with theperipheral zone; a photographic lens being attached to the camera body,an exit pupil of the photographic lens being optically aligned toproject light rays through the center zone of the center auto focusoptical system, at least two aperture zones being defined on the exitpupil by the at least two peripheral auto focus optical systems, each ofthe aperture zones being optically aligned to project light rays throughthe peripheral zone, at least one of the two aperture zones beinglocated at an upper side away from a central portion of the exit pupiland the other being located at a lower side away from the centralportion; the center auto focus optical system and the two peripheralauto focus optical systems, respectively, having at least onephotoelectronic device for producing an output signal; the output signalproduced by the photoelectronic device being adapted to move thephotographic lens automatically, thereby to bring the camera to be infocus; the each peripheral auto focus optical system comprising arotatable focus unit containing the camera body, and when a lens mountfor the photographic lens being attached to the camera body, therotatable focus unit being rotated mechanically, thus a bundle of rayscoming through the aperture zone being automatically made incident tothe zone of each peripheral auto focus optical system according to thephotographic lens characteristic.

According to the above-mentioned further embodiment for achieving thesecond object, even if the photographic lens is replaced with anotherlens having a different focal distance, the optical axis of theperipheral auto focus optical system can be mechanically andautomatically brought to be faced with the center of the exit pupil ofthe photographic lens by mounting action of the photographic lens to thecamera body so as to avoid the problem of vignetting.

Further objects of the present invention (and the invention of parentapplication Ser. No. 07/152,359) are directed to eye directiondetection. For example, a third object of the present invention is toprovide an eye direction detecting apparatus for a camera for detectingthe eye direction of a photographer.

A fourth object of the present invention is to provide an eye directiondetecting apparatus for a camera having an automatic focusing device, inwhich focusing zones of an auto focus optical system, which correspondto various focusing zones of the finder, are located in opticallygenerally conjugate positions with a plurality of focusing zonesdisposed within a view field of the finder, and focusing is made on anobject which is visually overlapped with the focusing zone correspondingto a selected one of the various focusing zones of the finder.

Another object of the present invention is to provide an eye directiondetecting apparatus for a camera for detecting the eye direction of aphotographer using a one-dimensional line sensor.

According to the teachings of the present invention, an eye directiondetecting apparatus for a camera having a light transferring system forguiding a beam of parallel light rays to an eye of a photographerincludes a light receiving system having a light receiving portion onwhich a first Purkinje image based on specular reflections of a corneaof the eye and reflecting light from a retina of the eye is formed, thelight receiving portion generating a light receiving output; and aprocessing circuit for detecting the eye direction of the eye based onthe light receiving output of the light receiving portion.

In embodiments of the present invention, the eye includes a pupil andthe pupil has a periphery, the light receiving portion includes aone-dimensional line sensor, the processing circuit establishes acoordinate corresponding to the periphery of the eye by processingoutput from the one-dimensional line sensor in one slice level, theprocessing circuit establishes a coordinate corresponding to the firstPurkinje image by processing output from the one-dimensional line sensorin another slice level, and the eye direction is detected by calculationcentral coordinate of the first Purkinje image and a central coordinateof the periphery of the pupil.

In certain embodiments of the present invention, the light receivingportion includes a primary line sensor and the processing circuitincludes means for separating the output from the one dimensional linesensor into a retina reflecting light corresponding output compositioncorresponding to a reflecting light from the retina and a first Purkinjeimage forming reflecting light corresponding output compositioncorresponding to a reflecting light for forming the first Purkinje imageand for finding a gravity position of the separated retina reflectinglight corresponding to the composition and the gravity position of firstPurkinje image forming reflecting light, thereby to detect the eyedirection, respectively.

According to the teachings of the present invention, the light receivingsystem may include a reimaging lens for reimaging reflecting light forforming the first Purkinje image on the one-dimensional line sensorbased on a corneal specular reflection, and the processing circuit mayinclude a correcting means for correcting a decrease of a peripheralportion incident light amount based on the light amount distributioncharacteristics of the reimaging lens.

In embodiments of the present invention, the position of the firstPurkinje image and the position of the pupil may be established by bitinverting the separated retina reflecting light corresponding outputcomposition and the first Purkinje image forming reflecting lightcorresponding output composition.

According to the teachings of the present invention, an eye directiondetecting apparatus of a camera includes a light transferring system forradiating a detecting light in the form of a parallel pencil of raystowards an eye looking into a finder magnifier, and a light receivingsystem having a light receiving portion for reimaging the detectinglight for forming a virtual image on the light receiving portion basedon corneal specular reflection of the eye, wherein the finder magnifieris provided at the side of the finder magnifier facing the eye with acoaxis forming optical member for making the optical axis of the lighttransferring system and the optical axis of the light receiving systemcoaxial.

In embodiments of the present invention, the light receiving system mayinclude a reducing lens and a reimaging lens disposed between the coaxisforming optical member and the light receiving portion, and the reducinglens may have at least one aspherical surface. The coaxis formingoptical member may be a mirror which permits visible light to passtherethrough and which has a reflecting and transmitting characteristicwith respect to infrared light. Alternatively, the coaxis forming aoptical member may be a prism. In such a case, the prism may have afirst transmitting surface facing the eye, a second transmitting surfaceopposite the first transmitting surface, and a reflecting surfacedisposed between the first transmitting surface and the secondtransmitting surface and facing the finder magnifier and, further,wherein first transmitting surface is slightly inclined with respect tothe coaxis.

According to the teachings of the present invention, an eye directiondetecting optical system includes a viewing area having a plurality ofzones to which the eye can be selectively directed, and means fordetermining to which of the plurality of zones the eye is directed, themeans for determining comprising means for compensating for a differencebetween determined eye direction and actual eye direction. The means forcompensating for a difference between determined eye direction andactual eye direction may include a means for compensating for adifference caused by light amount damping. The means for compensatingfor a difference caused by light amount damping may include-means fordetermining an amount of light amount damping. Such means, may alsoinclude means for generating a light amount correcting value based uponthe determined amount of light amount damping. Such means may stillfurther include either a read-only memory (ROM) element and/or anelectrically erasable programmable read-only memory (EEPROM) element.

In embodiments of the present invention, the eye may have a cornea and aretina, and the means for determining may further include means fordirecting light towards the eye, and means for generating a light amountdistribution including a first Purkinje image composition based oncorneal specular reflection and a retinal reflecting composition basedon reflecting light from the retina. The means for determining mayfurther include means for separating the first Purkinje imagecomposition and the retinal reflecting composition. The light amountdistribution may have a plurality of output levels, and the means forseparating may include means for establishing a plurality of zonelevels, and means for determining the number of output levelsterminating in each of the plurality of zone levels The means fordetermining may include a plurality of frequency registers one frequencyregister for each zone level. The means for determining may furtherinclude means for determining light amount distribution appearance in apredetermined zone.

In embodiments of the present invention, a boundary line may existbetween the first Purkinje composition and the retinal reflectingcomposition, and the means for determining may further include means forestablishing an at least one slice level in the vicinity of the boundaryline.

In embodiments of the present invention, the means for determining lightamount distribution appearance may include at least one frequencyregister having an output, and the means for establishing an at leastone slice level in the vicinity of the boundary line may operate basedupon the output of the at least one frequency register.

According to the teachings of the present invention, the light amountdistribution has a central or gravity position and the means fordetermining may further include means for calculating the gravityposition. The means for calculating the gravity position may includemeans for calculating a first phase difference between the separatedfirst Purkinje image composition and retinal reflecting composition,separating the first Purkinje image composition and the retinalreflecting composition, calculating a second phase difference betweenthe inverted first Purkinje image composition and retinal reflectingcomposition, and calculating the gravity position based upon the firstphase difference and the second phase difference.

According to the teachings of the present invention, an eye directiondetecting optical system includes means for directing light rays towardsthe eye; means for receiving light rays reflected by the eye, the meansfor receiving generating a light amount distribution; means forcompensating for damping of the amount of light received at the meansfor receiving; means for determining gravity position of the lightamount distribution, after compensation for light amount damping; andmeans for determining eye direction based upon the determined gravityposition. The means for compensating may include means for developing acorrection factor. The means for compensating may further include meansfor normalizing the correction factor to develop a correction value. Themeans for compensating may further include a means for storing thecorrection value, such as a read-only memory (ROM) or an electricallyerasable programmer read-only memory (EEPROM).

A system according to the present invention may further include meansfor correcting based upon the stored correction value.

In embodiments of the present invention wherein the eye has a cornea anda retina, the means for receiving may generate a light amountdistribution based on corneal specular reflection and reflecting lightfrom the retina.

According to the present invention, means for determining gravityposition of the light amount distribution may include means forseparating distribution effects resulting from corneal specularreflection and distribution effects resulting from reflecting light fromthe retina. The means for determining gravity position may furtherinclude means for establishing a slice level of the light amountdistribution.

In embodiments of the present invention, a boundary line may existbetween the distribution effects of the corneal specular reflection andthe distribution effects of the reflecting light from the retina. Insuch embodiments, means for establishing a slice level may establish theslice level in the vicinity of the boundary line. The means forestablishing a slice level may comprise means for providing a pluralityof zone levels, and means for selecting a zone level in which toestablish the slice level. In embodiments of the present invention, thelight amount distribution may have a varying output frequency and themeans for selecting a zone level in which to establish the slice levelmay select a zone level based on the varying output frequency. The meansfor selecting a zone level may include at least one frequency register,which at least one frequency register is adapted to provide an outputindicative of output frequency with a predetermined zone level. Incertain embodiments of the present invention, there may be a pluralityof frequency registers, one for each of the zone levels.

According to the teachings of the present invention, an eye directiondetecting apparatus includes means for directing light rays towards theeye; includes means for receiving light rays reflected by the eye, themeans for receiving generating a light amount distribution having agravity position; and processing means for calculating the gravityposition. In embodiments of the present invention, wherein the eye has acornea and a retina, the light amount distribution may have a cornealspecular reflection component and a retina reflection light component.In embodiments of the present invention, the processing means mayinclude means for determining a first phase difference between thecorneal specular reflection and component the said retina reflectinglight component. The processing means may further include means forinverting the corneal specular reflection component and the retinareflecting light component. The processing means may further includemeans for determining a second phase difference between the cornealspecular reflection component and the retina reflecting light component.In embodiments of the present invention, the processing means mayfurther include means for calculating the gravity position based on thefirst phase difference and the second phase difference.

According to the teachings of the present invention, an eye directiondetecting apparatus includes a light transferring system having anoptical axis; a light receiving system having an optical axis; means formaking the axis of the light receiving system and the optical axis ofthe light receiving system coaxial; and means for preventing refractedlight from forming a ghost image within the light receiving system. Inembodiments of the present invention, the means for making may includean optical member having at least two transmitting surfaces, each of theat least two transmitting surfaces having an identical angle ofinclination with respect to the coaxial axes. In embodiments of thepresent invention, the light transferring system may include means foremitting light, the light receiving system may include a light sensor,the apparatus may further include means for directing the emitted lightinto the eye, and light reflected from the eye may form a light amountdistribution on the light sensor. In embodiments of the presentinvention the eye may have a cornea and a retina and the light amountdistribution may have a corneal specular reflection component and aretinal reflecting light component.

Any, all, or any components of the systems and/or apparatus of thepresent invention may be incorporated into a camera. Such a camera mayhave an auto focusing capability.

A feature of an eye direction detecting apparatus for a camera accordingto the present invention is that a camera body is provided with a lighttransferring system for guiding a parallel pencil of rays to an eye of aphotographer; a light receiving system having a light for forming afirst Purkinje image based on a corneal specular reflection of the eyeand a reflecting light from the retina of the eye is present; and aprocessing circuit for detecting the eye direction of the eye of thephotographer based on a light receiving output of the light receivingportion is present.

A further feature of an eye direction detecting apparatus of a cameraaccording to the present invention is that the light receiving portioncomprises a one dimensional line sensor, and the processing circuitincludes means for separating the output from the primary line sensorinto a retina reflecting light corresponding output compositioncorresponding to a reflecting light from the retina and a first Purkinjeimage forming reflecting light corresponding output compositioncorresponding to a reflecting light for forming the first Purkinje imageand means for finding gravity position of the separated retinareflecting light corresponding to the composition and the gravityposition of a first Purkinje image forming reflecting light, thereby todetect the eye direction, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and new features of the invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic view of a conventional auto optical focusdetecting device of a single-lens reflex camera;

FIG. 2 is a perspective view schematically showing an arrangement of anauto focus optical system of FIG. 1;

FIG. 3 is a schematic view for explaining focusing by means of the autooptical focus detecting device;

FIG. 4 is a schematic view of a detecting output of a CCD of the autooptical focus detecting device;

FIG. 5 is a schematic view for explaining an arrangement of a zone to afinder according to a conventional optical focus detecting device;

FIG. 6 is a schematic view for explaining the photographing procedure inorder to obtain a photograph with a desired subject displaced to rightand left areas from the center by using the conventional auto opticalfocus detecting device;

FIGS. 7 through 20 are schematic views for explaining an eye directiondetecting optical system for use in an auto optical focus detectingdevice of a single-lens reflex camera according to the invention of theparent of the present case wherein:

FIG. 7 is a schematic view for explaining the detecting principle of aneye direction detecting optical system according to the invention of theparent of the present case and is a schematic view showing how a lightspot is formed when a parallel pencil of rays are projected to a convexmirror;

FIG. 8 is a schematic view showing how a first Purkinje image is formedwhen a parallel pencil of rays are projected to the cornea of an eye;

FIG. 9 is an enlarged view of an eye for explaining the relation betweenthe first Purkinje image and the center of the pupil;

FIGS. 10(A) and 10(B) are schematic views for obtaining the eyedirection from the first Purkinje image and the center of the pupil byarithmetic operation;

FIG. 11 is a plan view of a finder of an auto optical focus detectingdevice;

FIG. 12 is a schematic view showing the relation among an eye directiondetecting optical system and a finder magnifying lens used in an autooptical focus detecting device of a single-lens reflex camera accordingto the invention of the parent of the present case and the user's eye.

FIGS. 13 and 14 are detailed illustrations of an eye direction detectingoptical system;

FIG. 15 is an enlarged view of a reimaging lens of FIGS. 13 and 14;

FIG. 16 is a schematic view of the eye direction detecting opticalsystem;

FIG. 17 is a graph of a spherical aberration when a minifying lens ofFIGS. 13 and 14 is not an aspherical lens;

FIG. 18 is a graph of a distortion when the spherical aberration of FIG.17 is present;

FIG. 19 is a graph of a spherical aberration when the minifying lens ofFIGS. 13 and 14 is an aspherical lens;

FIG. 20 is a graph of a distortion when the spherical aberration of FIG.19 is present;

FIGS. 21 through 24 are schematic views for explaining a modifiedembodiment of the eye direction detecting optical system for use in theauto optical focus detecting device of a single-lens reflex cameraaccording to the present invention, wherein:

FIGS. 21 and 22 are schematic views showing the relation among thereimaging lens and the finder magnifying lens of the eye directiondetecting optical system for use in the auto optical focus detectingdevice of the camera according to the present invention, the user's eyeand a one-dimensional line sensor;

FIGS. 23 and 24 are schematic views for explaining the inconveniencewhen the one-dimensional line sensor is used as a light receivingelement of the eye direction detecting optical system;

FIG. 25 is an illustration for explaining a correction processing meansfor correcting the light amount damping at the peripheral portion of thereimaging lens;

FIG. 26 is a block diagram of a processing circuit having the correctionprocessing means;

FIG. 27 is a schematic view showing a relation between an actuallyobtained light amount distribution and the primary line sensor;

FIGS. 28 and 29 are illustrations for explaining an image separationprocessing means;

FIGS. 30 through 32 are graphs for explaining how to find the gravityposition of an image separation output distribution;

FIGS. 33 through 37 are illustrations for explaining still anotherexample of an optical system of the eye direction detecting apparatusaccording to the present invention, wherein;

FIG. 33 is an illustration for showing the constitution of an opticalsystem of the eye direction detecting apparatus;

FIG. 34 is an enlarged view of an important portion of the opticalsystem of the eye direction detecting apparatus shown in FIG. 33;

FIG. 35 is an enlarged view of the reimaging lens shown in FIG. 33;

FIGS. 36 and 37 are illustrations for explaining the opticalcharacteristics of the optical system of the eye direction detectingapparatus shown in FIG. 33;

FIGS. 38 through 40 are illustrations for explaining another example ofthe optical system shown in FIG. 33, wherein:

FIG. 38 is an optical diagram showing the constitution of an importantportion of the optical system of the eye direction detecting apparatus;and

FIGS. 39 and 40 are illustrations for explaining the opticalcharacteristics of the optical system shown in FIG. 38.

DETAILED DESCRIPTION OF THE INVENTION

For clarity and convenience, pertinent sections of the parentapplication of this application are discussed herein. Also for clarityand convenience, identical reference numerals are used to designateidentical or similar elements in both this application and thisapplication's parent.

It should be noted that the expression "eye direction" used in thisapplication means "the direction of a looking or viewing line of aneye", such a line being, of course, an imaginary one. Alternativeexpressions for this concept are "direction of line of sight" and "thedirection towards which an eye is looking". The concept described by allof these expressions should be kept in mind and understood when theshort expression "eye direction" is encountered in this application.

As discussed in this application's parent, an eye direction detectingoptical system which is used in an auto optical focused detecting deviceof a single lens reflex camera is described with references to FIGS.7-20.

A method for detecting an eye direction is described, for example, in anarticle entitled "Psychological Physic of Vision", written by MitsuoIkeda. When it is applied to a camera, only the direction of the user'seye must be detected. In other words, the parallel movement of theuser's eye with respect to a view finder of a camera should not bedetected. The reasons are as follows. In case the parallel movement ofthe eye is detected together with the detection of the eye direction,the information on the eye direction is overlapped on that of theangular direction. Therefore, it would be difficult for the camera tosense in which zone the user is looking. If an eye direction detectingoptical system which is also able to detect the parallel movement isemployed, the relative distance between the optical axis of the finderof the camera and the revolving center of an eye ball of the user mustbe kept constant. However, in view of the popularity of hand held typecameras, this is practically impossible since the eye is relativelytrembled sideward with respect to the finder 16.

An eye direction detecting optical system for detecting the eyedirection only in the angular direction is introduced, for example, in"Optical Engineering" of 1974, 7/8 Month, Vol. 23, No. 4, P339-342,Subtitle "Fixation Point Measurement by the Oculometer Technique".

The principle of an eye direction detecting optical system introduced inthis article is that, when a parallel pencil of rays P parallel to anoptical axis lx is radiated to a convex mirror 230, as shown in FIG. 7,an image of a light source located in an optically infinite distance isproduced as a light point at a middle point Q between a center R ofcurvature of, the convex mirror 230 and an intersecting point K Wherethe optical axis lx intersects the mirror surface. When the parallelpencil of rays parallel to the optical axis lx is radiated to a cornea232 of a human eye 231 as shown in FIG. 8, an image of a light sourcelocated in an optically infinite distance is also produced at a lightpoint (this light point is hereinafter referred to as "first Purkinjeimage PI") at the middle point Q between the center R of curvature ofthe cornea 230 and a corneal vertex K'. 233 denotes an iris, 234 denotesthe center of a pupil, and reference character S denotes the revolvingcenter of an eye ball.

When the optical axis lx of the bundle of rays P illuminating the cornea232 is in alignment with the eye direction l'x showing the direction ofthe human eye, the center 234 of the pupil, the first Purkinje image PI,the center R of curvature of the cornea 232, and the revolving center Sof the eye ball are located on the optically, axis lx. Regarding thecamera, it is impossible to assume that the revolving center S of theeye ball is located on the optical axis lx of the view finder. However,it is presumed here that the revolving center S of the eye ball islocated on the optical axis lx and the eye ball is located on theoptical axis lx and the eye ball is sidewardly revolved about therevolving center S. Then, as shown in FIG. 9, a relative gap is producedbetween the center 234 of the pupil and the first Purkinje image PI.Further, it is presumed that the eye is revolved by an angle θ withrespect to the optical axis lx and the length of the perpendicular lineextending from the center 234 of the pupil to the ray of light which ismade incident perpendicularly to the cornea 232 is denoted by d. Thefollowing relation can be obtained:

    d=k.sub.1 ·sin θ                            (1)

wherein k₁ is a distance from the center 234 of the pupil to the centerR of curvature of the cornea 232. Although there are individualdifferences, according to MIL-HDBK-141 "OPTICAL DESIGN" edited by theU.S. Department of Defense, the distance k₁ is about 4.5 mm. Referencecharacter H denotes an interesting point where the perpendicular lineextending from the center 234 of the pupil to the ray of light P' whichis made perpendicularly incident to the cornea 232 intersects the ray oflight P'.

As apparent from the above relation (1), since the distance k₁ is known,if the length d is found, the revolving angle θ can be obtained.

In view of the fact that the intersecting point H and the first Purkinjeimage PI are located on the ray of =light P', the parallel pencil ofrays P are radiated toward the cornea 232 and if the ray of light P"reflected and returned in the direction parallel to the incident bundleof rays among the specular reflection from the cornea 232 is detected,and if the relation between the center 234 of the pupil and the firstPurkinje image PI is found, the revolving angle θ of the eye can beobtained.

Therefore, assume the parallel pencil of rays P are projected to theeye. If the periphery or boundary 234' of the pupil with the iris 233appears as a silhouette based on the light reflected by the eye fundus,or retina and the first Purkinje image PI are imaged on the lightreceiving element such as, for example, the solid photosensitive elementas shown in FIGS. 10(A) and 10(B), the output of the received light hasa peak at the place corresponding to the first Purkinje image on thelight receiving element and the place corresponding the light reflectedby the eye fundus becomes a trapezoidal shape. Therefore, thecoordinates i₁ , i₂ corresponding to the periphery 234' of the pupil arefound by a slice level SL. Then, the coordinates PI₁ , PI₂ correspondingto the first Purkinje image PI are found by a slice level SL₂. Then, adifference d'=PI'-i' between the coordinates i' and the coordinates PI'corresponding to the center 234 of the pupil is calculated from therelations (2) and (3) set forth hereunder. If the power of the detectingoptical system is denoted by m here, the distance d can be found fromthe following relation (4):

    i'=(i.sub.1 +i.sub.2)/2                                    (2)

    PI'=(PI.sub.1 +PI.sub.2)/2                                 (3)

    d=d'/m                                                     (4)

Therefore, if such eye direction detecting optical system is employed,it can automatically determine the zone which is being viewed among theplurality of zones provided by the finder 16.

In the description of the principle, the center of each coordinate isfound by arithmetic means. However, in view of the strength of the lightreceived, or luminance thereof the center of the coordinate may be foundby weighted mean.

A specific example of an eye direction detecting optical system which isused in an auto optical focus detecting device of a single-lens reflexcamera according to the present invention will now be described.

In FIG. 12, 240 denotes a pentagonal prism built in a camera, 241 aquick return mirror, 242 a focusing plate, 243 a condenser lens, 244 afinder magnifying lens, 245 an eye of the user, and lx the optical axisof the aforementioned finder optical system. In this example, the findermagnifying lens 244 comprises magnifying lenses A and B.

The camera is provided with a detecting optical system 246 for detectingthe direction of the user's eye looking through the finder or findereyepiece element at the opposite side of the finder magnifying lens 244with the pentagonal prism 240 disposed therebetween. In FIG. 12, aframework 247 of the eye direction detecting optical system 246 isshown.

The eye direction detecting optical system 246, as shown in FIGS. 13 and14, has an infrared light source 248 such as, for example, an infraredlight emitting diode for emitting an infrared light. The infrared lightis projected to the user's eye 245 as a parallel pencil of rays througha half mirror 249, a minifying lens 250, a compensator prism 251, apentagonal prism 240, and a finder magnifying lens 244. By this, thefirst Purkinje image PI is formed based on the specular reflection ofthe cornea 232. Infrared light is employed in this embodiment so as notto dazzle the user with the illumination of the detecting optical system246. Similarly, the minifying lens 250 is employed for the reasons thatthe optical path length of the detecting optical system 246 is made asshort as possible so as to be compactly contained in the camera, andthat since only the infrared reflecting light parallel to the opticalaxis lx is employed, the light volume reflected by the eye 245 isconsidered to be small, and the reflecting light is imaged on as small adimension as possible on the light receiving surface of the lightreceiving element as an image receiving element as will be described soas to increase the sensitivity of the light receiving surface of thelight receiving element.

Of the light reflected by the cornea 232 of the eye 245, the bundle ofrays parallel to the bundle of incident rays are guided to the halfmirror 249 through finder magnifying lens 244 pentagonal prism 240compensator prism 251, and minifying lens 250, then guided to areimaging lens 252 by the half mirror 249, and then imaged on atwo-dimensional solid photosensitive element 253 (such as, for example,a two-dimensional area CCD), as the image receiving element by thereimaging lens 252. The reimaging lens 252, as shown in FIG. 15, isprovided with a mask 254. The mask 254 is formed with an opening 255.The center of the opening 255 is located in the center Y of curvature ofthe reimaging lens 252. The diameter of the opening 255 is about 0.2 mmin this embodiment.

The user's eye 245 is usually placed on an eye point. The solidphotosensitive element 253 and the pupil of the user's eye 245, asschematically illustrated in FIG. 16, are in optically conjugateposition through finder magnifying lens 244, minifying lens 250, and thereimaging lens 252. On the solid photosensitive element 253, theperiphery 234' of the pupil is formed as a silhouette together with thefirst Purkinje image PI by the light reflected on the eye fundus. Then,the receiving light output of the solid photosensitive element 253, asshown in FIG. 14, is amplified by the amplifier 256, then converted to adigital signal by an analog-digital converter 257, and then temporarilystored in a memory 259 of a microcomputer 258. The memory 259 ismemorized with a distance k₁ as an information. The information of thedistance k₁ and the information of the receiving light output are calledto an arithmetic circuit 260, then processed based on the relations (1)through (4) to find the revolving angle θ, and then a selected signalmeaning which zone has been selected is output to a driver 261 from therevolving angle θ. And, when the CCD of the auto focus optical systemcorresponding to the selected zone is driven by the driver 261, adistance to the subject to be photographed which is seen overlapped withthe zone intended by the user can be automatically found.

If the distance (the height of an image), as shown in FIG. 11, from thecenter Ox of the view field (the center of a focusing screen) of thefinder 16 to the centers Oy and Oz of the zones at both right and leftsides is represented by y, and if a focal distance of the findermagnifying lens 244 is represented by f, the following relation isobtained;

    y=f tan θ                                            (5)

If the relation (5) is substituted with the relation (1), the followingrelation is obtained;

    y=f d/(k.sub.2 ' cos θ)                              (6)

that is, y is proportional to d/(k₂ ' cos θ). This means that even ifthe distortion of an image formed on the image receiving element 253 iseliminated, the value of y can not be linearly found from the value ofd; in other words, a nonlinearity is present.

In the case of a 35 mm camera, the image height y of a plurality ofzones is considered to be about from 6 mm to 9 mm at the largest due tovignetting, etc.

In this embodiment, it is presumed that the eye direction detectingoptical system 246 transmits the image of the pupil having thenonlinearity to the image receiving element 253 located behind thesystem 246 as it is and that the length d detected by the imagereceiving element 253 is proportional to the image height y. Then, it ismerely detected in the longer side by from 0.7 to 1.6% than the actuallength d. Therefore, it does not adversely affect the selection of thezone at all. However, from the view point that the accuracy of the eyedirection detecting optical system must be improved, it is preferablethat the nonlinearity is not present. In such case, it can be correctedby the microcomputer. However, if the distortion is present in theoptical system itself, the measurement becomes incorrect. Therefore, thedistortion of the optical system must be eliminated as a minimumrequirement.

Therefore, in Order to make the spherical aberration of the minifyinglens 250 small, the plane 250a near the finder magnifying lens 244 isformed in an aspherical plane, and the focal position of the minifyinglens 250 is positioned in the center Y of curvature of the reimaginglens 252. In this way, if the minifying lens 250 is formed in anaspherical plane and if the focal point of the minifying lens 250 ispositioned in the center Y of curvature of the reimaging lens 252, theopening 255 is brought to be in the center Y of curvature of thereimaging lens 252. Thus, a distortion free optical system can beobtained which is much preferable as an eye direction detecting system.

Next, one example of the designing of such eye direction detectingoptical system will be described.

First, a distance from the magnifying lens A to an eye point is set to14.7 mm, the central thickness of the magnifying lens A is set to 4.98mm, the radius of curvature of the plane at the eye point side of themagnifying lens A is set to 181.168 mm of a convex, the radius ofcurvature of the plane at the side facing with the magnifying lens B ofthe magnifying lens A is set to -25.500 mm of a convex, and therefractive index of the magnifying lens A is set to 1.69105. And, adistance between the magnifying lenses A and B is set to 3.01 mm on theoptical axis lx. Further, the central thickness of the magnifying lens Bis set to 4.10 mm, the radius of curvature of the plane at the sidefacing with the pentagonal prism 240 of the magnifying lens B is set to-48.140 mm of a convex, and the refractive index of the magnifying lensB is set to 1.79175. Further, a distance between the plane 240a of thepentagonal prism 240 and the magnifying lens B is set to 3.21 mm, alength from the plane 240a of the pentagonal prism 240 to the plane 240bis set to 28.00 mm on the optical axis lx, the radius of curvature ofeach plane 240a, 240b is set to ∞, and the refractive index of thepentagonal prisms 240 is set to 1.51260. Next, a space between the plane251a of the compensator prism 251 and the plane 240b of the pentagonal:prism 240 is established to 0.10 mm, and a space between the plane 251bof the compensator prism 251 and the plane 250a of the minifying lens250 is also established to 0.10 mm. The length of the planes 251b and251a of the compensator prism 251 is set to 2.00 mm on the optical axislx, the radius of curvature of each plane 251a, 251b is set to ∞, andthe refractive index of the compensator prism 251 is set to 1.51260.

The minifying lens 250 is designed as such that the radius of curvatureof the plane 250a is 12.690 mm (k₃ =-3.00) of a convex, the centralthickness is 2.00 mm, and the refractive index is 1.48716. The radius ofcurvature of the other plane 250b of the minifying lens 250 is set to-200.000 mm of a convex, and a space between the reimaging lens 252 andthe plane 250b is set to 11.48 mm.

The radius of curvature of the plane 252a of the reimaging lens 252 isset to 1.520 mm of a convex, the radius of curvature of thee plane 252bis set to ∞, the central thickness of the reimaging lens 252 is set to1.52 mm, and the refractive, index is set to 1.48716 which is the sameas that of the minifying lens 252. Since the mask 254, which has theopening 255 having the diameter of 0.2 mm, is bonded to the plane 252b,the space between the mask 254 and the plane 252b is 0 mm, the thicknessof the mask is set to 0.04 mm, and the space between the mask 254 to thelight receiving surface of the image receiving element 253 is set to1.46 mm. The mask 254 and the light receiving surface of the imagereceiving element 253 is set to ∞, and spaces among the respectiveoptical elements are filled with air.

k₃ denotes an aspheric spherical coefficient and has the followingrelation with the sag X: ##EQU1## wherein h denotes the height from theoptical axis px, and c denotes an inverse number of the radius ofcurvature of the minifying lens 250.

In case the minifying lens 250 is not aspherical, spherical aberrationis taken place as shown in FIG. 17, and a distortion is present as shownin FIG. 18. However, if an eye direction detecting optical system whichis designed in a way as mentioned above, the spherical aberration isimproved as shown in FIG. 19. As a result, the distortion is alsoimproved as shown in FIG. 20.

Although a specific embodiment has been described in the foregoing, itmay be designed such that an LED corresponding to each zone 17, 26, 27is provided within the view field of the finder 16, and the LEDcorresponding to the selected zone is blinked so as to confirm whetherit is the zone intended by the user.

Next, an example of the improvement of an eye direction detectingoptical system for use in an auto optical focus detecting device of asingle-lens reflex camera according to the present invention will bedescribed.

In the aforementioned case, a two-dimensional solid photosensitiveelement is employed as the image receiving element. However, since thearrangement of the solid photosensitive element is two-dimensional, itis expected that the scan processing time for scanning the solidphotosensitive element takes a long time. In addition, the cost becomeshigh. In one with a plurality of zones 17, 26 and 27 linearly arrangedas shown by an arrow Z in FIG. 11, it is conceivable that aone-dimensional line sensor can be employed in which the photoelectronicelement is disposed in the direction corresponding to the direction inwhich the zones 17, 26 and 27 are arranged. However, if such aone-dimensional line sensor is employed, the following problems occur.FIGS. 23 and 24 are illustrations for explaining these problems. In FIG.24, 244 denotes a finder magnifying lens, 252 a reimaging lens, and 102a one-dimensional line sensor as the image receiving element. As shownin FIG. 23, when the optical axis lx of the eye direction defectingoptical system 246, i.e., the optical axis lx of the finder magnifyinglens 244 and the eye direction axis l'x are in alignment, the pupilimage 234a as the silhouette (periphery) of the pupil, and the firstPurkinje image PI are formed on the one-dimensional line sensor 102.Therefore, an eye direction detection can be carried out normally.However, when the human eye 245 is moved in the vertical direction withrespect to the camera body, as shown in FIG. 24, the pupil image 234a asthe silhouette and the first Purkinje image PI are out of theone-dimensional line sensor 102. Therefore, the eye direction detectionis impossible to carry out normally and is thus inconvenient.

FIGS. 21 and 22 are illustrations for explaining the constitution foravoiding the inconvenience when the one-dimensional line sensor isemployed.

In this one-dimensional line sensor 102, as shown in FIGS. 21 and 22,the photoelectronic elements 102 are arranged in a directioncorresponding to the direction Z wherein a plurality of zones arearranged. An anomarphic device including a cylindrical lens is employedhere as the reimaging lens 252. As shown in FIGS. 21 and 22, a mask 254is provided to the plain face side of the cylindrical lens. The mask 254is provided with an opening 255. The center of the opening 255 islocated in the center Y of curvature of the reimaging lens 252. Theopening 255 is, in this illustration, a rectangular slit. The extendingdirection of the slit 255 is perpendicular to the arranging direction ofthe photoelectronic elements of the one-dimensional line sensor 102. Thereimaging lens 252 has a spherical surface disposed at the side of thefinder magnifying lens 244.

The user's eye 245 is usually placed on the eye point, and theone-dimensional line sensor 102 and the pupil of the user's eye, asschematically illustrated in FIG. 16, are in optically conjugaterelation with each other through finder magnifying lens 244, minifyinglens 250 and reimaging lens 252. Therefore, the one-dimensional linesensor 102 is formed with the pupil image 234a as the silhouette due tothe light reflected by the eye fundus together with the first Purkinjeimage PI, The reimaging lens 252 is the cylindrical lens and is disposedas such that a vertically elongated first Purkinje image PI and pupilimage 234a as the silhouette are formed in the direction perpendicularto the arranging direction of the one-dimensional line sensor 102 on aplane including the one-dimensional line sensor 102. Therefore, even ifthe eye 245 is moved in the vertical direction with respect to thecamera body A₁ as shown in FIG. 22, at least one portion of therespective images PI and 234a are formed on the one-dimensional linesensor 102. Further, since the opening 255 of the mask 254 is also anelongated slit extending in the direction perpendicular to the arrangingdirection of the photoelectronic elements 102a of the one-dimensionalline sensor 102, the pupil image 234a and first Purkinje image PI formedon the plane including the one-dimensional line sensor 102 become longerin the vertical direction, perpendicular to the arranging direction.Therefore, the eye direction detection can be carried out reliably.Therefore, if the receiving light output of each photoelectronic element102a of the one-dimensional line sensor 102 is amplified by theamplifier 256 and converted to a digital signal by the analog-digitalconverter 257 to be subjected to a predetermined processing, the eyedirection can be detected.

In the aforementioned embodiment, although a cylindrical lens isemployed as the reimaging lens 252, a toric lens may be employed.

Another example of a processing circuit of an eye direction detectingapparatus 246 will now be described.

In view of the facts that an optical system of the eye directiondetecting apparatus 246 is built in a camera body and that costincreases are to be avoided as much as possible it is desirable that theoptical system be as simple as possible and reimaging lens 252 ispreferably a single lens.

However, in the event that such a reimaging lens 252 is used, if lightof a uniform light amount distribution is made incident on the reimaginglens 252, the amount of the light imaged on the light receiving surfaceof a primary line sensor 253 is damped at the peripheral portion asschematically shown in FIG. 25. In FIG. 25, the two-dotted chain line G₁shows the light amount distribution when the light amount is not damped,the broken line G₂ shows the light amount distribution when the lightamount is damped, and l_(x) shows the optical axis of the optical systemof the eye direction detecting apparatus 246 as described.

Where such light amount damping is present, if the gravity position ofthe light amount distribution is found based on the output of theone-dimensional line sensor 253, there is a risk that such found gravityposition is displaced from the actual gravity position and, therefore,if the eye direction is established through calculation using such foundgravity position, an error will occur between the actual eye directionand such obtained eye direction.

In case the angle of the eye direction which is to be distinguished islarge, the error based on the light amount damping is allowable.However, the error based on the light amount damping cannot bedisregarded as the angle of the eye direction, which is to bedistinguished, becomes smaller. Any error based on the light amountdamping is preferably removed, if possible, in order to correctly detectthe eye direction through calculation.

To this end, in the processing circuit, there is provided means forfinding the light amount damping beforehand and storing a light amountcorrecting value in a read-only memory or ROM, which will be described.

That is, the output distribution of the one-dimensional line sensor 253corresponding to that of the light amount damping becomes something likethat shown by reference G₃ of FIG. 25. In the figure, referencecharacter i denotes an i^(th) photoelectric element 253a, j denotesj^(th) photoelectric element 253a, x_(i) denotes the output of an i^(th)photoelectric element 253a and x_(j) denotes the output of a j^(th)photoelectric element 253a. Presume that the j^(th) photoelectricelement 253a is located on the optical axis l_(x). In other words,presume that the j^(th) photoelectric element 253a is a central addressbetween a-address and b-address. In this case, it can be anticipatedthat the output of the j^(th) photoelectric element 253a is the largest.

Therefore, the various output from the a-address photoelectric element253a to the b-address photoelectric element 253a are found and thecorrection factor H_(i) is found.

The following relational expression is obtained among the correctionfactor H_(i), the output X_(i) and the output X_(j).

    H.sub.i X.sub.i =X.sub.j                                   (5)

In order to normalize the correction factor H_(i), the correction factorH_(i) is divided by X_(j) to find a correction value H₁ ' and thecorrection value H_(i) is stored in the ROM of the processing circuitshown in FIG. 26.

    H.sub.i '=H.sub.i /H.sub.j                                 (6)

If such normalized correction value H_(i) ' is corrected by multiplyingit with the output of each address (from a-address to b-address)actually obtained, the output distribution corresponding to the dampedlight amount distribution is corrected as shown by reference characterG₄. In other words, there can be obtained a uniform output distributionG₄, in which the light amount damping based on the affection of theperipheral portion of the imaging lens 252 with respect to a uniformlight is compensated for.

Furthermore, if a correction value based on the light amountdistribution obtained when a parallel uniform light is made incidentfrom the finder magnifier 244 is stored for use in a writable andrewritable EEPROM, there can be effected the correction including theerror caused by the light amount distribution in the state where theoptical elements other than the reimaging lens 252 of the optical systemare included, as well as the irregularity of sensitivity of the variousphotoelectric elements 253a of the primary line sensor 253 itself.Therefore, if such correction is performed, the specification regardingthe optical characteristic of the one dimensional line sensor 253 itselfcan be loosened, and a cost reduction based on the improvement of theyield of production can be obtained.

In order to find a gravity position of the light amount distribution forforming the first Purkinje image PI based on the corneal specularreflection and a light amount distribution gravity position of areflecting light from the retina respectively, the output of the primaryline sensor 253 must be separated into a retina reflecting lightcorresponding output composition which corresponds to the retinalreflecting light and a first Purkinje image forming reflecting lightcorresponding output composition which corresponds to the first Purkinjeimage PI.

That is, the actual light amount distribution becomes something likethat shown by the solid line G₅ of FIG. 27. Therefore, if the processingis carried out without being separated into the retina reflecting lightcorresponding output composition G₆ and the first Purkinje image formingreflecting light corresponding output composition G₇, a gravity position(coordinate or address) including both of them can be found, but thecenter 234 of the pupil and the center of the first Purkinje image PIcannot be found.

In such a case, in order to separate the retina reflecting lightcorresponding output composition G₆ and the first Purkinje image formingreflection light corresponding output composition G₇ as correctly aspossible, the slice level SL must be established in the vicinity of theboundary line. To this end, a plurality of zone levels ZN are providedand the output frequency of the photoelectric element 253a is checked.

In this embodiment 8 pieces of the zone level ZN are provided as shownin FIG. 28. The 8 pieces of the zone level ZN are denoted by referencecharacters ZN₁ through ZN₈.

And, in order to check the output frequency of the photoelectricconverting element 253a, 8 pieces of appearance frequency register R₁through R₈ are provided in such a manner so as to correspond with the 8pieces of zone level ZN₁ through ZN₈. The bit number of the appearancefrequency registers R₁ through R₈ is 8. And, the output of eachphotoelectric element 253a from the a-address to the b-address issuccessively input into the appearance frequency registers R₁ throughR₈. For example, since the output of the a-address is "O" the contentsof all appearance frequency register are "O". If the output of thephotoelectric converting element 253a of j-address is an outputcorresponding; to 2⁶, the content of the appearance frequency registerR₂ becomes "00000010" and the contents of the remaining frequencyregisters are "O". For example, if the output of the photoelectricelement 253a of the i+1-address is larger by a portion corresponding to1 bit than the output 2⁶ (00000010) of the photoelectric convertingelement 253a of the i-address, the content of the appearance frequencyregister R₃ becomes "10000010" (2⁶).

Therefore, by paying attention to the high-order 3 bits of theappearance frequency registers R₁ through R₈, a "+1" is output from theappearance frequency registers R₁ through R₈ when the data of thecontent of the high-order 3 bits include at least one "1". And, theoutput of the photoelectric element 253a of each address (i=a through b)is input, and the output of each appearance frequency register R₁through R₈ is incrementally counted every time the content of thehigh-order 3 bits includes at least one "1". When the content of thehigh-order 3 bits does not include a "1", it is not incrementallycounted. In this way, if the appearance frequency registers R₁ throughR₈ are incrementally counted every time the photoelectric element 253aof each address is output, in the case or the output distributionschematically shown, since the number of the photoelectric elements 253ahaving the output level somewhere between the zone level ZN₂ and thezone level ZN₃ is the largest, the increment count number of theappearance frequency register R₃ is expected to become the largest.

Therefore, regarding the output distribution of the photoelectricelements 253a of all addresses, it is judged whether or not theincrement count number of the appearance frequency registers R₁ throughR₈ becomes the largest after the increment count. And, the zone level ZNcorresponding to the appearance frequency registers R₁ through R₈ wherethe increment count number becomes the largest is established as theslice level S1 using all bits of the register. Thus, the count range ofeach register is from 0 (00000000) to 255 (11111111). If this slicelevel is used, the retina reflecting light corresponding outputcomposition G₆ and the first Purkinje image forming reflecting lightoutput composition G₇ can be separated.

The width of the zone level ZN₁ through ZN₈ is established correspondingto the nozzle based on the reflection from the retina, and thecomposition of this nozzle level can be removed through a low passfilter. However, it can also be removed by means of software processingin which the zone levels ZN₁ through ZN₈ are overlapped.

Accordingly, the 8 bit output signal from each sensor cell differs fromthe counts of appearance frequency register. Specifically, an 8 bitoutput signal is obtained from each sensor cell. The upper 3 bits of the8 bit output signal is then used to determined a zone level, and thecount of the appearance frequency register that corresponds to thedetermined zone level is increased. This process is then repeated forthe remaining cells in the sensor.

For example, as shown in FIG. 29, the sum of the increment count numberof the adjacent appearance frequency registers R₁ through R₈ areobtained, (using all 8 bits) and the appearance frequency register, inwhich the sum thereof is the largest, is judged. In the example shown inFIG. 29, since the sum of the appearance frequency register R₃ and theappearance frequency register R₄ is the largest, it is judged that theincrement count number of the appearance frequency register R₄ is thelargest.

Since the intermediate level appears most frequently among the retinareflecting light corresponding output composition G₆, regarding theestablishment of the level SL, the appearance frequency registers R₁ andR₈ are not taken into consideration from the beginning.

In this way, the zone level ZN₄ corresponding to the appearancefrequency register R₄ can be found. Herein, it is decided beforehandthat it refers to the first Purkinje image forming reflecting lightcorresponding output composition G₇ when the content of the appearancefrequency register R₄ is "00000001" or more, and that it refers to theretina reflecting light corresponding output composition G₆ when thecontent of the appearance frequency register R₄ is "00000110" or less.

Due to the foregoing arrangement, the slice levels SL₁ and SL₂ as shownin FIG. 27 can be established in the vicinity of the boundary linebetween the retina reflecting light corresponding output composition G₆and the first Purkinje image forming reflecting light correspondingoutput composition G₇ based on the content of the appearance frequencyregister R₄.

In this way, when the slice levels SL₁ and SL₂ are established and theoutput composition corresponding to the light amount distributioncharacteristic as shown in FIG. 27 is sliced to perform the imageseparation processing, a separation output as shown in FIG. 30 can beobtained. In FIG. 30 the solid line G₈ shows the retina reflecting lightcorresponding separation output, whereas the solid line G₉ shows thefirst Purkinje image forming reflecting light corresponding separationoutput. In this embodiment, the configuration of the retina reflectinglight corresponding separation output G₈ is trapezoid because theaforementioned correction processing has been performed before theoutput of the one dimensional line sensor 253 is separated into theretina reflecting light corresponding separation output G₈ and the firstPurkinje image forming reflecting light corresponding separation outputG₉. Therefore, if the gravity position of the retina reflecting lightcorresponding separation output G₈ is represented by X₁ and if thegravity position of the first Purkinje image forming reflecting lightcorresponding separation output G₉ is represented by X₂, the distance d"from the center 234 of the pupil to the first Purkinje image can befound from the relation d"=X₂ -X₁.

As a calculation algorithm for finding the gravity position, one, inwhich the output of PSD (position sensor diode) is realized by asoftware calculation, is used. That is, as shown in FIGS. 31(a) and31(b), the convolution of the image separation output corresponding tothe heavy worth functions W_(A) and W_(B) is obtained and, thereafter,integrated. For example, the convolution of the image separation outputG₉ and the heavy worth functions W_(A), W_(B) as shown in FIGS. 31(c)and 31(d) is taken to obtain the multiplication outputs C_(A) and C_(B).Then, the multiplication outputs C_(A) and C_(B) are integrated toobtain the integration values S_(A) and S_(B).

Then, the gravity position X can be obtained from the followingrelation;

    X=S.sub.F *{(S.sub.A -S.sub.B)/(S.sub.A +S.sub.B)+1}×1/2

wherein S_(F) is the distance from the origin O.

In this method, the multiplication of every bit is required in order totake the convolution. In recent time, since microcomputers having amultiplying function are widely used, the gravity position can beobtained by this method.

However, if this gravity position X is to be found by software, there isan accompanying disadvantage in that it takes quite a bit of time forcalculation.

Therefore, a processing means which can calculate the gravity position Xin a comparatively short time is employed in this embodiment.

The obtained separation outputs G₈ and G₉ are bit inverted with respectto the position coordinates to produce the inverse separation outputs G₈' and G₉ ' as shown in FIG. 30.

According to this method, by calculating the phase difference betweenthe separation outputs G₈ and G₉ before inverse and the separationoutputs G_(8') and G_(9') after inverse, the gravity position can beobtained with generally the same degree of accuracy as that mentionedabove. This phase difference can be found by a calculating methodsimilar to the function system calculation of a phase differencedetecting method which is used in a single-lens reflex camera having anauto-focus optical system known per se. In this calculating method, ithas been known that there can be obtained an accuracy in such degree asone divided by a figure of several times of ten through one divided byseveral hundreds of a resolving power of a picture element of a sensorby means of interpolating calculation.

As opposed to a case where an entirely unexpected object is taken, inthe case of this eye direction detecting apparatus 246, the patternwhich will be obtained can be anticipated. When the reflecting lightfrom the retina and the reflecting light forming the first Purkinjeimage are formed into a spot image on the one dimensional line sensor253, symmetrical separation outputs G₈ ' and G₉ ' can be obtained.Therefore, as shown for example in FIG. 32, if the separation output G₈' is a simple pattern, the center O_(E) of the rising positioncoordinate and the falling position coordinate can be anticipated to begenerally the gravity position. Therefore, when the phase difference isto be detected, if a calculation is made only with respect to before andafter the center O_(E), the time for calculation can be shortened.

To be more concrete, the output of the primary sensor 253 is representedby (a). Herein, n denotes the address of the photoelectric element 253aof the primary line sensor. By paying attention to the n- and n+1addresses, the differential output E(n) can be obtained from thefollowing equation;

    E(n)=S(n+1)-S(n)

In this way, there can be obtained an integrate output as shown in FIG.32.

Next, if the coordinate where E(n) becomes the largest is represented byt₁ and if the coordinate where E(n) becomes the smallest is representedby t₂, it can be anticipated that the gravity position is generally (t₂+t₂)/2.

Therefore, the inverse separation output at the time when the positionalcoordinate is inversed is represented by G₃ " to generate the differenceoutput R(n). The integrate output B_(E) ' corresponding to thedifference output R(n) becomes something like that shown by the solidline. If all bit numbers are represented by m here and if thecorrelation method calculation for finding the phase difference of R(n)with respect to S(n) is carried out with respect to before and afterm-(t₁ +t₂), the gravity position can be found. In the same manner, thephase difference between B_(E) and B_(E) ' can be found.

If the phase difference of R(n) with respect to S(n) or the phasedifference between B_(E) and B_(E) ' is represented by t, the gravityposition from the central coordinate O_(E) ' of the sensor of S(n) canbe found from t/2.

By using such calculation algorithm, there can be realized an eyedirection detecting apparatus with high accuracy.

Unless the method for finding the phase difference between B_(E) andB_(E) ' is employed, since R(n) corresponds with the address of thememory in which S(n) is stored, if the data is called in the reverseorder from the address, it is not necessary to form a memory zone forgenerating R(n) and, thus, the memory can be saved.

Furthermore, since the object is to find the largest and smallestaddresses regarding the generation of E(n) and since the object is notto obtain E(n), the generating zone thereof is not necessary, either.

In the optical system of the eye direction detecting apparatus 246 ofthe above-mentioned example, since the light transferring system 246Aand the light receiving system 246B are built in the camera body at theopposite side of the finder magnifier with the penta prism 240 as theboundary line, the reflecting light based on the refracting surfaces ofvarious optical elements which constitute the light transferring system246A and the light receiving system 246B is guided to the lightreceiving system 246B as a ghost, and a ghost as well as the firstPurkinje image PI are formed on the primary line sensor 253 of the lightreceiving system 246B. Therefore, there still remains a problem in thatit is difficult to distinguish the ghost and the first Purkinje imagePI.

Therefore, an optical system of an eye direction detecting apparatus ofa camera which is designed so that the ghost is not guided to the lightreceiving system 246B by every means will now be described.

FIGS. 33 through 37 illustrate an optical system of an eye directiondetecting apparatus of a camera which is designed so that the ghost isnot guided to the light receiving system 246B by every means. In thefigures, identical component elements to those of the optical systemshown in FIG. 13 are denoted by identical or similar reference numerals.

In this embodiment, the light transferring system 246A includes a lightsource 248 for emitting an infrared light, a total reflection mirror149, and a collimator lens 150. The collimator lens 150 is aspherical atits surface. The infrared light emitted by the light source 248 isreflected by the total reflection mirror 149 and guided to thecollimator lens 150. The collimator lens 150 is provided at its outgoingside surface with a diaphragm 151. The collimator lens 150 has such afunction as to convert the infrared light emitted by the light source248 into a parallel pencil of rays.

At the side where an eye 245 of the finder magnifier 244 is faced with,there is provided a coaxis forming, or light path overlapping opticalmember 152 for making the optical axis l_(i) of the light transferringsystem 246A and the optical axis l_(j) of the light receiving system246B as a coaxis. In this embodiment, the coaxis forming optical system152 comprises a rectangular parallelepiped comprising prisms 154 and 155having a reflecting surface 153. The coaxis forming optical member 152has a transmitting surface 156 facing the eye 245, a transmittingsurface 157 opposite the transmitting surface 156 with the reflectingsurface 153 sandwiched therebetween, and a transmitting surface 157'facing the collimator lens 150. The transmitting surface 156 is providedwith a mask 158.

In this embodiment, in order to avoid the ghost based on the reflectionat various transmitting surfaces of the coaxis forming optical member152, the transmitting surfaces 156 and 157 are slightly inclined withrespect to the optical axis l_(x), whereas the transmitting surface 157'is slightly inclined with respect to the optical axis l_(i). Theinclination angles of the various transmitting surfaces 156, 157 and157' with respect to the various optical axes l_(x) and l_(i) are 1° inthis embodiment. Since the various transmitting surfaces 156, 157 and157' have the same inclination angles, it becomes the same as the statewhere the parallel plane is inserted, and the aberration due to theinclination is hardly changed.

The reflecting surface 153 employed in this embodiment is of the typefor semi-transmitting an infrared light and for transmitting a visiblelight. Since the reflecting surface 153 transmits a visible light, thephotographer can see an image of the object formed on a focusing plate242. The parallel pencil of rays passed through the diaphragm 151 isreflected by the reflecting surface 153 in the direction toward the eye245 and projected to the eye 245 of the photographer placed on an eyepoint. In this embodiment, although it is used as the coaxis formingoptical member 152, a mirror of the type for semi-transmitting aninfrared light and for transmitting a visible light may be employed.

The corneal specular reflection beam of light for forming the firstPurkinje image PI and the reflecting beam of light from the retina areguided again to the coaxis forming optical member 152, passed throughthe reflecting surface 153 and then guided to the finder magnifier 244.The finder magnifier 244 comprises lenses 244a and 244b in the samemanner as mentioned.

In this embodiment, the light receiving system 246B comprises acompensator prism 159, a reducing lens 250, a total reflection mirror161, a reimaging lens 252, and a primary line sensor 253. The reimaginglens 252, as shown in FIG. 35 in its enlarged scale, is provided on thesurface at the side facing With the primary line sensor 253 with a mask254 which is of the same constitution as already mentioned.

In this embodiment, the light receiving system 246B is preferablyprovided with no distortion and has preferably a generally uniform lightamount distribution on the primary line sensor 253 in view of the objectheight. If the optical system is constituted in a way as will bedescribed hereinafter, as shown in FIG. 36, the light amountdistribution on the primary line sensor 253 can be generally equallycovered within the range of the required object height. In addition, asshown in FIG. 37, the distortion can be made 1 μ or less.

By way of example only, presented below are various design values thatmay be used in light transferring system 246A:

Radius of curvature of the outgoing surface of the light source 248 . .. infinite;

Distance along the optical axes of the outgoing surface of the lightsource 248 and the total reflection mirror 149 . . . 7.7 mm;

Distance between the total reflection mirror 149 and the surface A ofthe collimator lens 150 . . . 7.3 mm

COLLIMATOR LENS 150

Radius of curvature of the surface A . . . 10.00 mm

Radius of curvature of the surface B . . . -28.00 mm

Refractive index . . . 1.48304

Center thickness . . . 4.00 mm

Distance along the optical axes between the mask 151 and the surface Bof the collimator lens 150 . . . 0.00 mm

MASK 151

Thickness . . . 0.04 mm

Radius of curvature . . . infinite

Distance along the optical axes of the mask 151 and the transferringsurface . . . 0.66 mm

TRANSMITTING SURFACE 157'

Radius of curvature . . . infinite

Inclination with respect to the optical axis l_(i) . . . 1°

Refractive index of the coaxis forming optical member 152 . . . 1.50871

Distance along the optical axes from the transmitting surface 157' tothe transmitting surface 156 . . . 12 mm

TRANSMITTING SURFACE 156

Radius of curvature . . . infinite

Inclination with respect to the optical axis l_(x) . . . 1°

Distance along the optical axes from the transmitting surface 156 to thecornea 232 . . . 13 mm

Radius of curvature of the cornea 232 . . . 7.980 mm

The surface A of the collimator lens 150 is aspherical and designed byfinding the sag amount X from the following imaging formula of anaspheric lens; ##EQU2## wherein c is an inverse number of the radius ofcurvature of the surface A of the collimator lens 150, h is the objectheight from the optical axis l_(i), and k is an aspheric coefficient,and K=-3.165, α₄ =-2.95×10⁻⁵, and α₆ =0.

By way of example only, presented below are various design values thatmay be used in light receiving system 246B:

Radius of curvature of the cornea 232 . . . -7.980 mm

Distance along the optical axes from the cornea 232 to the transmittingsurface 156 . . . 13 mm

TRANSMITTING SURFACE 156

Inclination with respect to the optical axis l_(x) . . . -1°

Radius of curvature . . . infinite

Refractive index of the coaxis forming optical member 152 . . . 1.50871

Distance along the optical axes of the transmitting surfaces and 157 . .. 10 mm

TRANSMITTING SURFACE

Inclination with respect to the optical axis l_(x) . . . -1°

Radius of curvature . . . infinite

Distance along the optical axes from the transmitting surface 157 to thesurface A of the lens 244a . . . 0.60 mm

LENS 244a

Radius of curvature of the surface A . . . 115.895 mm

Center wall thickness . . . 1.2 mm

Refractive index . . . 1.69747

Radius of curvature of the surface B . . . 29.210 mm

LENS 244b

Radius of curvature of the surface B . . . 29.210 mm

Center wall thickness . . . 4.92 mm

Refractive index . . . 1.61187

Radius of curvature of the surface C . . . -47.880 mm

Distance along the optical axes from the surface C to the surface A ofthe pentagonal prism 240 . . . 1.00 mm

PENTAGONAL PRISM 240

Radius of curvature of the surface A . . . infinite

Refractive index . . . 1.50871

Radius of curvature of the surface B . . . infinite

Inclination of the surface B with respect to the optical axis l_(k) . .. -24°

Distance along the optical axes from the surface A to the surface B . .. 28.80 mm

Distance along the optical axes of the surface B and the surface A ofthe compensator prism 159 . . . 0.14 mm

COMPENSATOR PRISM 159

Radius of curvature of the surface A . . . infinite

Inclination of the surface A with respect to the optical axis l_(j) . .. -24°

Radius of curvature of the surface B . . . infinite

Distance along the optical axes of the surfaces A and B . . . 3 mm

Refractive index . . . 1.50871

Distance from the surface A to the mask 159' . . . 0 mm

MASK 159'

Thickness . . . 0.04 mm

Radius of curvature . . . infinite

Distance of the optical axes from the mask 159' to the surface A of thereducing lens 250 . . . 0.10 mm

REDUCING LENS 250

Radius of curvature of the surface A . . . 11.716 mm

Wall thickness . . . 2.50 mm

Radius of curvature of the surface B . . . -60.140 mm

Refractive index . . . 1.48304

Distance along the optical axes from the surface B to the totalreflection mirror 161 . . . 3.00 mm

Radius of curvature of the total reflection mirror 161 . . . infinite

Distance along the optical axes from the total reflection mirror 161 tothe reimaging lens 252 . . . 7.60 mm

REIMAGING LENS 252

Radius of curvature of the surface A . . . 1.520 mm

Refractive index . . . 1.48304 mm

Center wall thickness . . . 1.520 mm

Radius of curvature of the surface B . . . infinite

Distance from the surface B to the mask 254 . . . 0.00 mm

MASK 254

Radius of curvature . . . infinite

Wall thickness . . . 0.04 mm

The surface A of the reducing lens 250 is aspheric and designedaccording to the afore-mentioned formula but under the condition ofK=-1.25, α₄ =-8×10⁻⁵, and α₆ =-10⁻⁶.

FIGS. 38 through 40 illustrate a second embodiment of an eye directiondetecting optical apparatus of a camera according to the presentinvention. In this embodiment, a light transferring system 246A isdisposed opposite a finder magnifier 244 with a pentagonal prism 240placed therebetween, and a light receiving system 246B is disposed atthe side of a transmitting surface 157' of a coaxis forming opticalmember 152, so that the infrared light emitted by a light source 248 isguided to the finder magnifier 244 through a compensator prism 159 andthe pentagonal prism 240. The infrared light is converted into aparallel pencil of rays by the finder magnifier 244 and projected to theeye 245. The beam of light for forming the first Purkinje image PI basedon the corneal specular reflection of the eye 245 and the reflectinglight from the retina are reflected by a reflecting surface 153 of thecoaxis forming optical member 152 and then guided to the light receivingsystem 246B. All the remaining optical component elements are generallythe same as the first embodiment and the optical characteristics thereofare also generally the same as the first embodiment as shown in FIGS. 11and 12. Therefore, design values thereof are merely stated hereunder.

(1) DESIGN VALUES OF THE LIGHT TRANSFERRING SYSTEM 246A: (EXAMPLES ONLY)

Radius of curvature of the outgoing surface of the light source 248 . .. infinite

Distance along the optical axes of the outgoing surface of the lightsource 248 and the total reflection mirror 149 . . . 17 mm

Radius of curvature of the total reflection mirror 149 . . . infinite

Distance along the optical axes of the total reflection mirror 149 andthe mask 159' . . . 3 mm

MASK 159'

Wall thickness . . . 0.04 mm

Radius of curvature . . . infinite

Distance between the mask 159' and the surface B of the compensatorprism 159 . . . 0.00 mm

COMPENSATOR PRISM 159

Radius of curvature of the surface B . . . infinite

Distance between the surfaces A and B . . . 3 mm

Radius of curvature of the surface A . . . infinite

Inclination of the surface A with respect to the optical axis l_(i) . .. 24°

Distance along the optical axes of the surface A and the surface B ofthe pentagonal prism 240 . . . 0.14 mm

PENTAGONAL PRISM 240

Radius of curvature of the surface B . . . infinite

Inclination of the surface B with respect to the optical axis l_(i) . .. 24°

Refractive index . . . 1.50871

Radius of curvature of the surface A . . . infinite

Distance between the axes from the surface A to the surface B . . .28.80 mm

Distance between the axes of the surface A and the surface C of the lens244b . . . 1.00 mm

LENS 244b

Radius of the curvature of the surface C . . . 47.880 mm

Radius of the curvature of the surface B . . . -29.210 mm

Center wall thickness . . . 4.92 mm

Refractive index . . . 1.61187

LENS 244a

Radius of the curvature of the surface B . . . -29.210 mm

Radius of the curvature of the surface A . . . -115.895 mm

Center wall thickness . . . 1.2 mm

Refractive index. . . 1.69747

Distance along the optical axes of the surface A and the transmittingsurface 157 . . . 0.60 mm

TRANSMITTING SURFACE 157

Radius of the curvature . . . infinite

Inclination with respect to the optical axis l_(i) . . . 2°

Refractive index of the coaxis forming optical member 152 . . . 1.50871

Distance along the optical axes from the transmitting surface 157 to thetransmitting surface 156 . . . 10 mm

TRANSMITTING SURFACE 156

Radius of the curvature . . . infinite

Inclination with respect to the optical axis l_(x) . . . 2°

Distance along the optical axes from the transmitting surface 156 to thecornea 232 . . . 13 mm

Radius of the curvature of the cornea 232 . . . 7.980 mm

(2) DESIGN VALUES OF THE LIGHT RECEIVING SYSTEM 246B (EXAMPLES ONLY):

Radius of the curvature of the cornea 232 . . . -7.980 mm

Distance along the optical axes from the cornea 232 to the transmittingsurface 156 . . . 13 mm

TRANSMITTING SURFACE 156

Radius of the curvature . . . infinite

Inclination with respect to the optical axis l_(x) . . . -2°

Distance along the optical axes from the transmitting surface 156 to thetransmitting surface 157' . . . 12 mm

Refractive index of the coaxis forming optical member 152 . . . 1.50871

TRANSMITTING SURFACE 157'

Inclination with respect to the optical axis l_(j) . . . -2°

Radius of the curvature . . . infinite

Distance along the optical axes from the transmitting surface 157' tothe mask 151 . . . 0.66 mm

Distance between the mask 151 and the reducing lens 250 . . . 0.00 mm

MASK 151

Radius of the curvature . . . infinite

Wall thickness . . . 0.04 mm

REDUCING LENS 250

Radius of the curvature of the surface A . . . 28.00 mm

Wall thickness . . . 4.00 mm

Radius of the curvature of the surface B . . . -10.00 mm refractiveindex . . . 1.48304

Distance along the optical axes from the surface B to the totalreflection mirror 161 . . . 7.30 mm

Radius of the curvature of the total reflection mirror 161 . . .infinite

Distance along the optical axes of the total reflection mirror 161 andthe surface A of the reimaging lens 252 . . . 5.70 mm

REIMAGING LENS 252

Radius of the curvature of the surface A . . . 2.00 mm

Refractive index . . . 1.48304

Center wall thickness . . . 2.00 mm

Radius of the curvature of the surface B . . . infinite

Distance between the surface B to the mask 254 . . . 0.00 mm

MASK 254

Radius of the curvature . . . infinite

Thickness . . . 0.04 mm

The surface B of the reducing lens 250 is aspheric and is designed fromthe afore-mentioned formula but under the condition that K=-3.165, α₄=2.95×10⁻⁵, and α₆ =0.

As those skilled in the art should appreciate, an optical system of aneye direction detecting apparatus of a camera constructed according tothe teachings of the present invention will not allow a ghost to beguided to the internal light receiving system.

Many modifications and variations of this invention are possible inlight of the above teachings It therefore to be understood that withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically described.

We claim:
 1. An eye direction detecting device built into a finder of acamera having a pentagonal prism and an eyepiece, said eye directiondetecting device comprising:means for guiding a beam of light towards aneye of a photographer looking at said finder; means for detecting areflected beam of light reflected from the eye of the photographer, saiddetecting means providing an output signal; and means for determining adirection in which the eye gazes with respect to an image formed on saidfinder based on said output signal of said detecting means, wherein saidguiding means and said detecting means are both mounted proximate anupper side of said camera proximate said pentagonal prism, said finderbeing built into said camera.
 2. The eye direction detecting device ofclaim 1, wherein said guiding means comprises a light source foremitting said beam of light.
 3. The eye direction detecting device ofclaim 2, wherein said light source comprises an infrared light source.4. The eye direction detecting device of claim 1, wherein said detectingmeans comprises a plurality of detecting elements that detect saidreflected beam of light reflected from the eye of the photographer. 5.The eye direction detecting device of claim 1, wherein said detectingmeans comprises a one-dimensional line sensor having a plurality ofdetecting elements.
 6. The eye direction detecting device of claim 5,wherein a cornea of the eye and said one-dimensional line sensor are ina substantially conjugate relation with each other.
 7. An eye directiondetecting device built into a finder of a camera having a pentagonalprism and an eyepiece, said eye direction detecting devicecomprising:means for guiding a beam of light towards an eye of aphotographer looking at said finder; means for detecting a reflectedbeam of light reflected from the eye of the photographer, said detectingmeans providing an output signal; means for determining a direction inwhich the eye gazes with respect to an image formed on said finder basedon said output signal of said detecting means, wherein said guidingmeans and said detecting means are both mounted proximate an upper sideof said camera proximate said pentagonal prism, said finder being builtinto said camera; and a re-imaging lens that elongates an image formedby said beam of light reflected from the eye of the photographer.
 8. Theeye direction detecting device of claim 7, wherein said detecting meanscomprises a one-dimensional line sensor having a plurality of detectingelements.
 9. The eye direction detecting device of claim 8, wherein saidre-imaging lens comprises a cylindrical re-imaging lens that elongatessaid formed image in a direction perpendicular to a direction ofarrangement of elements of said sensor.
 10. The eye direction detectingdevice of claim 5, wherein said one-dimensional line sensor has a narrowwidth in a first direction of elements of said sensor and a broad widthin a second direction perpendicular to said first direction.
 11. The eyedirection detecting device of claim 1, wherein at least one of saidguiding means and said detecting means is mounted opposite a side ofsaid eyepiece, at least a portion of a reflecting surface of saidpentagonal prism facing said at least one of said guiding means and saiddetecting means transmitting light from said at least one of saidguiding means and said detecting means.
 12. An eye direction detectingdevice for a SLR camera, comprising:a finder built into said SLR camera,an image of an object to be photographed being formed on said finder;means for guiding a beam of light towards an eye of a user gazingtowards said finder; means for receiving a reflected beam of lightreflected from the eye of the user, said receiving means providing anoutput signal corresponding to a direction to which the eye of the usergazes in said finder; and means for determining a direction in which theeye gazes according to said output signal, said receiving means having aminifying lens to reduce an optical path length of said eye directiondetecting device.
 13. The eye direction detecting device of claim 12,wherein said beam of light comprises an infrared beam of light.
 14. Theeye direction detecting device of claim 12, wherein said guiding meanscomprises a light source for emitting said beam of light.
 15. The eyedirection detecting device of claim 12, wherein said receiving meanscomprises a one-dimensional line sensor.
 16. The eye direction detectingdevice of claim 12, said minifying lens comprising a lens having anaspherical surface on a first side, and a radius of curvature of saidfirst side is smaller than of a second side.
 17. An eye directiondetecting device for a SLR camera, comprising:a finder built into saidSLR camera, an image of an object to be photographed being formed onsaid finder; means for guiding a beam of light towards an eye of aphotographer gazing towards said finder; means for receiving a reflectedbeam of light that is reflected from the eye of the photographer, saidreceiving means providing an output signal corresponding to a directionto which the eye of the user gazes in said finder; and means fordetermining a direction in which the eye gazes according to said outputsignal of said receiving means, said receiving means having at least onelens element, one surface of said at least one lens element having aradius of curvature smaller than a radius of curvature of another sideof said at least one lens element that is aspherical.
 18. The eyedirection detecting device of claim 17, said at least one lens elementcomprising a minifying lens having an aspherical surface provided on onesurface.
 19. The eye direction detecting device of claim 17, furthercomprising a prism associated with said camera, said guiding means andsaid detecting means being mounted proximate an upper side of saidcamera proximate said prism.
 20. An eye direction detecting device builtinto a finder of a camera having a pentagonal prism and an eyepiece,said eye direction detecting device comprising:means for guiding a beamof light towards an eye of a photographer; means for detecting areflected beam of light reflected from the eye of the photographer andproviding an output signal, said detecting means further comprisingmeans for separating said reflected beam of light from an optical pathof said finder, said separating means comprising an element having areflecting surface distinct from said pentagonal prism that separatessaid reflected beam of light from said optical path of said finder; andmeans for determining a direction in which the eye gazes based on saidoutput signal of said detecting means.
 21. The eye direction detectingdevice of claim 20, wherein said separating means comprises a prism. 22.The eye direction detecting device of claim 20, wherein said guidingmeans and said detecting means are mounted proximate said pentagonalprism.
 23. The eye direction detecting device of claim 20, wherein atleast one of said guiding means and said detecting means is mountedopposite a side of said eyepiece, at least a portion of a reflectingsurface of said pentagonal prism facing said at least one of saidguiding means and said detecting means transmitting light from said atleast one of said guiding means and said detecting means.
 24. An eyedirection detecting device of a camera, comprising:means for guiding abeam of light towards an eye of a photographer; means for detecting areflected beam of light reflected from the eye of the photographer, saiddetecting means comprising a sensor with a plurality of sensor cells;and means for determining a threshold level for deriving a firstPurkinje image from outputs of said plurality of sensor cells, saiddetermining means counting numbers of said sensor cells in each of aplurality of output zone levels, said threshold level being determinedas a maximum output level count.
 25. The eye direction detecting deviceof claim 24, wherein said determining means comprise appearancefrequency registers that count numbers of said plurality of sensor cellsin each output zone level, said determining means determining saidthreshold level as one of said output zone levels that correspond to ahighest frequency register.
 26. An eye direction detecting device builtinto a finder of a camera having a pentagonal prism and an eyepiece,said eye direction detecting device comprising:means for guiding a beamof light towards an eye of a photographer; means for detecting areflected beam of light reflected from the eye of the photographer andproviding an output signal, said detecting means comprising means forseparating said reflected beam of light from an optical path of saidfinder, and means for deflecting said reflecting beam of light; andmeans for determining a direction in which the eye gazes based on saidoutput of said detecting means, wherein said detecting means is mountedin said finder of said camera.
 27. The eye direction detecting device ofclaim 26, wherein said deflecting means comprises a mirror.
 28. The eyedirection detecting device of claim 26, wherein said guiding means andsaid detecting means are mounted proximate said pentagonal prism. 29.The eye direction detecting means of claim 26, wherein said guidingmeans further comprises means for generating said beam of light.
 30. Aneye direction detecting device built into a finder of a camera,comprising:means for defining a plurality of zones corresponding toframes that can be seen in said finder to which an eye of a photographercan be selectively directed, said plurality of zones being arranged insaid finder along a predetermined direction, said plurality of zonescomprising parts of a field of view of said finder; means for guiding abeam of light towards the eye of the photographer; means for receiving abeam of light reflected from the eye of the user and for providing anoutput signal, said receiving means comprising a sensor having arectangular shape with long sides directed along the predetermineddirection; and means for determining which zone of said plurality ofzones the eye is gazing at in accordance with said output signal of saidreceiving means.
 31. The device of claim 30, wherein said sensorcomprises a one-dimensional line sensor.
 32. The eye direction detectingdevice of claim 30, wherein said plurality of zones can be seen throughsaid finder.
 33. The eye direction detecting device of claim 30, whereinsaid predetermined direction comprises a direction aligned with a majordirection of said field of view of said finder.
 34. The eye directiondetecting device of claim 30, wherein said camera includes a pluralityof focus detecting systems, said plurality of zones corresponding todetecting zones of said plurality of focus detecting systems.
 35. An eyedirection detecting device, comprising:a finder assembly of a camera,said finder assembly having an eyepiece element; a light source; meansfor directing a beam of light from said light source through saideyepiece element so that said beam of light impinges upon aphotographer's eye positioned proximate said eyepiece element; a sensorfor detecting a beam of light reflected from the photographer's eye andwhich passes through said eyepiece element, said sensor comprising meansfor producing an output signal; means for processing said output signalof said sensor for determining a direction in which the photographer'seye gazes; a re-imaging lens for re-imaging said beam of light reflectedfrom said eye through said eyepiece element onto said sensor; and aminifying lens for reducing an optical path length of said eye directiondetecting device.
 36. An eye direction detecting device built into afinder of a camera having a pentagonal prism and an eyepiece, said eyedirection detecting device comprising:means for guiding a beam of lighttowards an eye of a photographer looking at said finder, said guidingmeans including means for controlling a width of said beam of light tobe at least a width of a cornea of the eye of the user at a point wheresaid beam of light impinges on the eye so that said beam of light coversthe cornea of the eye, regardless of an eye movement in a directionperpendicular to an optical axis of said finder; means for detecting areflected beam of light reflected from the eye of the photographer, saiddetecting means providing an output signal; and means for determining adirection in which the eye gazes with respect to an image formed on saidfinder based on said output signal of said detecting means, said finderbeing built into said camera.
 37. The eye direction detecting device ofclaim 36, wherein said guiding means comprises a light source foremitting said beam of light.
 38. The eye direction detecting device ofclaim 37, wherein said light source comprises an infrared light source.39. The eye direction detecting device of claim 36, wherein saiddetecting means comprises a plurality of detecting elements that detectsaid reflected beam of light reflected from the eye of the photographer.40. The eye direction detecting device of claim 36, wherein saiddetecting means comprises a one-dimensional line sensor having aplurality of detecting elements.
 41. The eye direction detecting deviceof claim 40, wherein a cornea of the eye and said one-dimensional linesensor are in a substantially conjugate relation with each other. 42.The eye direction detecting device of claim 36, further comprising are-imaging lens that elongates an image formed by said beam of lightreflected from the eye of the photographer.
 43. The eye directiondetecting device of claim 42, wherein said re-imaging lens comprises acylindrical re-imaging lens that elongates said formed image in adirection perpendicular to a direction of arrangement of elements ofsaid sensor.
 44. An eye direction detecting device built into a finderof a camera, comprising:means for defining a plurality of zones arrangedin the finder to which an eye of a user can be selectively directed,said plurality of zones comprising parts of a field of view of saidfinder; means for guiding a beam of light towards the eye of the user;means for receiving a beam of light reflected from the eye of the userand for providing an output signal; and means for determining whichdirection and zone of said plurality of zones the eye gazes at inaccordance with said output signal of said receiving means.
 45. The eyedirection detecting device of claim 44, wherein said plurality of zonescorresponds to frames that can be seen in said finder.
 46. The eyedirection detecting device of claim 44, wherein said plurality of zonesare arranged in said finder along a predetermined direction.
 47. The eyedirection detecting device of claim 46, wherein said receiving meanscomprises a rectangular shaped sensor having long sides directed alongsaid predetermined direction.